Introduction: The forests of western Iran are among the natural ecosystems whose regeneration has been severely disrupted by anthropogenic and natural factors. Among these, livestock browsing is one of the most significant drivers of vegetation degradation and morphological alterations in plant species. This biotic stress can impair plant competitive ability by damaging photosynthetic organs, reducing growth, and altering leaf structure. This study was conducted to investigate the effects of livestock grazing on the anatomical traits of leaf stomata and trichomes in Prunus argentea (Lam.) Rehder, a shrub species native to the region. Given the limited experimental and laboratory-based studies on the micro-morphological responses of this species to environmental stressors, the present study aims to elucidate how browsing induces changes in leaf microstructure, thereby triggering distinct adaptive responses that may reflect divergent survival strategies under browsing pressure. Furthermore, the study identifies which leaf traits exhibit the highest degree of plasticity in response to the stress. The findings may contribute to improved forest management and conservation of valuable tree species that are also important forage resources.
Materials and Methods: In each of two study sites near Ilam City (Darreh-ye Arghavan and Choghasabz), three individual Prunus argentea shrubs exposed to continuous livestock browsing were randomly selected (six shrubs in total). For each selected shrub, leaf samples were collected from both lower branches (accessible to browsing animals) and upper branches (out of reach of browsers). Sampling was conducted along the dominant slope direction at each site. Overall, six samples per site (three shrubs × two vertical canopy positions) were collected. From each shrub, 10 leaves were randomly collected from lower (browsed-accessible) and 10 from upper (non- browsed) branches. To enhance observation of stomata and trichomes, photosynthetic pigments were removed from the abaxial leaf surface. Following staining and preparation of microscopic sections, 11 anatomical traits related to stomata, trichomes, and vein density were measured using a digital camera equipped with image analysis software. All measurements were repeated to ensure high repetition and accuracy.
Results: The results indicated that livestock browsing significantly altered most leaf anatomical traits. Specifically, the mean length and width of stomata, stomatal pore length, stomatal density, and stomatal pore index were significantly reduced under browsing pressure. In contrast, trichome dimensions, including length, width, and density, showed a significant increase in browsing conditions. Principal component analysis (PCA) revealed that traits such as stomatal density and stomatal pore index contributed most to the separation of non- browsed samples, whereas vein density and trichome width were more influential in distinguishing browsed samples. Furthermore, leaf trichome traits exhibited higher phenotypic plasticity compared to stomatal traits in Prunus argentea.
Conclusion: Overall, livestock browsing exerted significant effects on all anatomical traits of stomata and leaf trichomes, leading to notable changes in both the size and density of these structures. The high plasticity observed in trichome-related traits suggests a strong adaptive capacity of Prunus argentea in response to browsing-induced stress and altered environmental conditions. Therefore, anatomical modifications in leaves likely impact plant performance and physiological efficiency, potentially reducing overall productivity. These findings highlight the importance of considering plant structural plasticity in ecological restoration and sustainable forest management, particularly for species that are both ecologically and economically valuable.